It is known to perform speaker verification by first performing a process of enrolling a user to obtain a model of the user's speech. Then, when it is desired to determine whether a particular test input is the speech of that user, a first score is obtained by comparing the test input against the model of the user's speech. In addition, a process of score normalization may be performed. For example, the test input may also be compared against a plurality of models of speech obtained from a plurality of other speakers. These comparisons give a plurality of cohort scores, and statistics can be obtained describing the plurality of cohort scores. The first score can then be normalized using the statistics to obtain a normalized score, and the normalized score can be used for speaker verification.
However, the statistics describing the cohort scores will be heavily dependent on the other speakers whose speech was used to form the plurality of models, and this may give undesirable results, particularly when the test input is not well matched to the other speakers.